Observing the collapse of super-Bloch oscillations in strong-driving photonic temporal lattices

Super-Bloch oscillations(SBOs)are amplified versions of direct current(dc)-driving Bloch oscillations realized under the detuned dc-and alternating current(ac)-driving electric fields.A unique feature of SBOs is the coherent oscillation inhibition via the ac-driving renormalization effect,which is dubbed as the collapse of SBOs.However,previous experimental studies on SBOs have only been limited to the weak ac-driving regime,and the collapse of SBOs has not been observed.Here,by harnessing a synthetic temporal lattice in fiber-loop systems,we push the ac-field into a strong-driving regime and observe the collapse of SBOs,which manifests as the oscillation-trajectory localization at specific ac-driving amplitudes and oscillation-direction flip by crossing collapse points.By adopting arbitrary-wave ac-driving fields,we also realize generalized SBOs with engineered collapse conditions.Finally,we exploit the oscillation-direction flip features to design tunable temporal beam routers and splitters.We initiate and demonstrate the collapse of SBOs,which may feature applications in coherent wave localization control for optical communications and signal processing.

Incoherent non-Hermitian skin effect in photonic quantum walks

The non-Hermitian skin effect describes the concentration of an extensive number of eigenstates near the boundaries of certain dissipative systems.This phenomenon has raised a huge interest in different areas of physics,including photonics,deeply expanding our understanding of non-Hermitian systems and opening up new avenues in both fundamental and applied aspects of topological phenomena.The skin effect has been associated to a nontrivial pointgap spectral topology and has been experimentally demonstrated in a variety of synthetic matter systems,including photonic lattices.In most of physical models exhibiting the non-Hermitian skin effect full or partial wave coherence is generally assumed.Here we push the concept of skin effect into the fully incoherent regime and show that rather generally(but not universally)the non-Hermitian skin effect persists under dephasing dynamics.The results are illustrated by considering incoherent light dynamics in non-Hermitian photonic quantum walks.

Designing non-Hermitian real spectra through electrostatics

Non-hermiticity presents a vast newly opened territory that harbors new physics and applications such as lasing and sensing.However,only non-Hermitian systems with real eigenenergies are stable,and great efforts have been devoted in designing them through enforcing parity-time(PT)symmetry.In this work,we exploit a lesser-known dynamical mechanism for enforcing real-spectra,and develop a comprehensive and versatile approach for designing new classes of parent Hamiltonians with real spectra.Our design approach is based on a new electrostatics analogy for modifed non-Hermitian bulk-boundary correspondence,where electrostatic charge corresponds to density of states and electric felds correspond to complex spectral fow.As such,Hamiltonians of any desired spectra and state localization profle can be reverse-engineered,particularly those without any guiding symmetry principles.By recasting the diagonalization of non-Hermitian Hamiltonians as a Poisson boundary value problem,our electrostatics analogy also transcends the gain/loss-induced compounding of foating-point errors in traditional numerical methods,thereby allowing access to far larger system sizes.